CN114501862B

CN114501862B - Production method for improving flatness of COB (chip on board) product of rigid-flex printed circuit board and COB product thereof

Info

Publication number: CN114501862B
Application number: CN202210060989.XA
Authority: CN
Inventors: 黄顺俊; 卿志彬; 沈雷; 雷加兴; 陈世金; 冯冲; 韩志伟; 徐缓
Original assignee: BOMIN ELECTRONICS CO LTD
Current assignee: BOMIN ELECTRONICS CO LTD
Priority date: 2022-01-19
Filing date: 2022-01-19
Publication date: 2023-08-04
Anticipated expiration: 2042-01-19
Also published as: CN114501862A

Abstract

The invention discloses a production method for improving flatness of a Chip On Board (COB) product of a rigid-flex printed circuit board and the COB product thereof, and relates to a rigid-flex printed circuit board improvement technology. The scheme is provided for solving the problems that the thickness and the cost are increased due to the improvement of flatness in the prior art. The method comprises the steps of breaking the copper layer of the waste area at a certain distance; and adjusting the flexible plate extending out of the rigid plate into a structure of five heads and two tails. The method has the advantages that the stress of the rigid-flex printed circuit board can be released after the copper layer in the waste material area is broken; meanwhile, the number of the flexible plates is increased, the stress area can be increased, the suspension between the adjacent rigid plates is reduced, and the connection between the plates is firmer and the plates are not easy to warp. The whole scheme does not increase the total thickness of the rigid-flex printed circuit board and does not increase the manufacturing cost. On the contrary, because the copper layer in the waste area is broken, the window opening design of the solder resist ink layer becomes feasible, thereby reducing the use amount of halogen-free black oil and reducing the manufacturing cost.

Description

Production method for improving flatness of COB (chip on board) product of rigid-flex printed circuit board and COB product thereof

Technical Field

The invention relates to an improvement technology of a rigid-flex printed circuit board, in particular to a production method for improving the flatness of a COB product of the rigid-flex printed circuit board and the COB product thereof.

Background

COB packages are known as Chip On Board (COB) packages, and the corresponding electronic products are COB products. In the prior art, the general COB profile structure of the flex-rigid board 10 of COB products is shown in fig. 1 and 2. The edge of the rigid-flex board 10 is left with waste copper in the production process, which forms a closed annular copper layer. The board center is provided with a circuit design area, and the circuit function is achieved by interconnecting a plurality of rigid boards 30 on the board through flexible boards 33.

The rigidizer 30 includes a larger sized head portion 31 and a smaller sized tail portion 32 with a rigidized transition therebetween. The top end, the left end and the right end of the head and the bottom end of the tail extend out of the flexible plate 33 respectively to form a three-head and one-tail structure. Each flexible plate 33 is used to connect adjacent rigid plates 30.

The laminated structure of the rigid plate 30 and the flexible plate 33 is shown in fig. 3, in which the middle layer is a flexible double-sided FCCL and the outer layer uses two sheets of PP of No flow. The flatness requirements of COB products are very high, and the flatness of the finished products is usually required to be less than or equal to 0.03mm. However, the thickness of the finished product of the COB product is relatively thin, and is usually 0.30-0.45mm, so that the problems of warping and the like often occur, and the flatness cannot meet the index requirement.

There are two main types of conventional solutions in the industry for improving flatness of such products:

1, adding FR4 base materials, such as copper-clad plates, on the outer side of PP (Polypropylene) of the COB stack, wherein the thickness of a finished product is at least 100 mu m relatively thick, and meanwhile, the material and production process cost are increased;

2, a No flow PP with high TG (glass transition temperature) is selected, for example, the flatness of the PP with the TG value reaching 230 is relatively improved, but the cost of the PP with high TG value is much higher than that of the common PP, and the product competitiveness is directly reduced.

Disclosure of Invention

The invention aims to provide a production method for improving flatness of a COB product of a rigid-flex printed circuit board and the COB product thereof, so as to solve the problems in the prior art.

The invention relates to a production method for improving the flatness of a COB product of a rigid-flex printed circuit board, which comprises the step of breaking a copper layer in a waste area at a certain distance; and adjusting the flexible plate extending out of the rigid plate into a structure of five heads and two tails; the structure of the first five tail parts is specifically as follows: a flexible plate extends from the middle of the top end of the head part far away from the tail part of the rigid plate, and two flexible plates extend symmetrically from the left end and the right end of the rigid plate respectively to form a first fifth; the left end and the right end of the tail part are symmetrically extended with a flexible board to form a tail II; the flexible plates respectively extend out of the rigid plates and are respectively used for connecting the adjacent rigid plates.

The interval distance between the broken copper layers of the waste material area is 22-28 mm.

The copper layers of the scrap region were interrupted by a separation distance of 25mm.

The width of the broken copper layer of the waste area is 3-5 mm.

The width of the copper layer of the scrap region is 4mm.

When the solder resist ink layer is manufactured, a hollow window is arranged at the position where the copper layer in the waste material area is broken.

The COB product provided by the invention is prepared by the production method.

The production method for improving the flatness of the COB product of the rigid-flex printed circuit board and the COB product thereof have the advantages that the stress of the rigid-flex printed circuit board can be released after the copper layer in the waste material area is broken; meanwhile, the number of the flexible plates is increased, the stress area can be increased, the suspension between the adjacent rigid plates is reduced, and the connection between the plates is firmer and the plates are not easy to warp. The whole scheme does not increase the total thickness of the rigid-flex printed circuit board and does not increase the manufacturing cost. In contrast, the copper layer in the waste area is broken, so that the window opening design of the solder resist ink layer becomes feasible, the use amount of halogen-free black oil is reduced, and the manufacturing cost is reduced.

Drawings

FIG. 1 is a schematic diagram of the appearance and structure of a rigid-flex board of a COB product in the prior art;

FIG. 2 is a schematic diagram of the external connection structure of a rigid-flex printed circuit board in the prior art;

FIG. 3 is a schematic view of the cross-sectional stacking of the K-K direction of FIG. 2;

FIG. 4 is a schematic diagram of the appearance and structure of the rigid-flex printed circuit board manufactured by the manufacturing method of the invention;

FIG. 5 is a schematic diagram of the external connection structure of the rigid-flex printed circuit board according to the present invention;

FIG. 6 is a schematic view of the external connection structure of the rigid-flex printed circuit board and each comparative example according to the present invention;

FIG. 7 is a graph showing the comparison of flatness test data for the rigid-flex printed circuit board according to the present invention and each of the comparative examples;

fig. 8 is a comparison chart of windowing effects of the rigid-flex printed circuit board.

Reference numerals:

10-a rigid-flex board;

20-a copper layer of a waste area and 21-a hollow window;

30-rigidizer, 31-head, 32-tail, 33-flexplate.

Detailed Description

As shown in fig. 4, the production method for improving the flatness of the COB product of the flex-rigid board according to the present invention breaks the copper layer 20 in the waste area at the edge of the flex-rigid board 10. The interval between the interruptions can be controlled to a certain range, for example 22-28 mm; the width of the interruption can be about 3-5 mm. The specific spacing and width selection can be fully adjusted by those skilled in the art according to the overall size variation of the rigid-flex board 10. The present example performs the test at 25mm intervals and 4mm widths.

While the flexible panel 33 with the rigid panel 30 extending outwardly is adjusted from the existing first three-end to the first five-end, as shown in fig. 5.

For comparative illustration of the technical effect of varying the number of extensions of the flex 33, the present invention is also illustrated by providing 5 comparative examples, as shown in fig. 6.

Comparative example one: FIG. 6 (a) shows a three-head-to-tail structure of the prior art, i.e. the top end of the head 31 is provided with a flexible board 33 extending from the middle, and the left and right ends are provided with flexible boards 33 respectively; and the bottom end of the tail portion 32 extends a flexible plate 33.

Comparative example two: fig. 6 (b) shows a three-head and two-tail structure, which is different from the first comparative example in that the tail portion 32 is changed to have two flexible boards 33 extending from the left and right ends, and the tail portion 32 extends in the same manner as the five-head and two-tail structure of the present invention.

Comparative example three: fig. 6 (c) is a structure of four heads and four tails, which is different from the first comparative example in that the head 31 is changed to have two flexible plates 33 extending from the left and right ends, and the extension of the top is canceled.

Comparative example four: fig. 6 (d) shows a structure of the first four-tail two, which combines the head 31 extension of the third comparative example and the tail 32 extension of the second comparative example.

Comparative example five: fig. 6 (e) shows a five-head and one-tail structure, which combines the head 31 extension of the present embodiment and the tail 32 extension of the first comparative example.

This embodiment: fig. 6 (f) shows a structure of five heads and two tails, i.e. a flexible board 33 extends from the middle of the top end of the head 31 far from the tail 32, and two flexible boards 33 extend symmetrically from the left and right ends to form five heads; a flexible board 33 is symmetrically extended from the left and right ends of the tail to form a tail two.

The data for the flatness obtained for the 5 comparative example structures and the present example structure were tested in large quantities as shown in fig. 7, where the ordinate unit is mm.

	Comparative example one	Comparative example two	Comparative example three	Comparative example four	Comparative example five	This embodiment
							Maximum flatness	0.0324713	0.0317955	0.0368983	0.0346155	0.0318168	0.0294665
Minimum flatness value	0.0242673	0.0228725	0.0256297	0.0263392	0.0232805	0.0221628
							Average value of flatness	0.0283693	0.027334	0.031264	0.0304774	0.0275487	0.0258147
Change interval	0.008204	0.008923	0.0112686	0.0082763	0.0085363	0.0073037

As can be seen, the flatness is improved by increasing the number of extensions of the flexible plate 33 in the tail portion 32. However, the greater the number of extensions of the flexible board 33 in the head 31 is, the more excellent the flatness of the rigid-flex board 10 is. In particular, when the existing structure of the third head is increased to the fourth head, the flatness is found to be deteriorated by those skilled in the art. There is no incentive to make incremental adjustments to the number of flexible panels 33 in this trend, as well as to set the particular location.

However, the invention provides a unique structure of five heads and two tails, and instead obtains better technical effects compared with all the comparative examples: the maximum value of flatness is less than 0.03mm, and the variation interval is the smallest in various structures, so that unexpected technical effects are obtained.

In order to further improve the flatness of the flex-rigid board 10, when the flex-rigid board 10 is produced, a hollow window 21 is provided at a position where the copper layer 20 breaks in the waste region during the process of producing the solder resist ink layer. The solder resist ink layers are SM-T and SM-B in fig. 3. On the basis of the first five-end and second-end of the invention, the effect comparison is carried out by windowing and non-windowing, and as shown in figure 8, the ordinate unit is also mm.

When the empty window 21 is not provided, the flatness data is the same as fig. 7 (f). However, after the hollow window 21 is arranged, the stress of the rigid-flex printed circuit board 10 can be further released, the adhesive force of halogen-free black oil is reduced, and the effect that the maximum flatness is less than or equal to 0.022mm is obtained. The maximum flatness is even smaller than the minimum value without windowing, and the variation interval is greatly reduced as shown in the figure, which shows that the controllability of the batch finished products is obviously improved.

The COB product provided by the invention is provided with the rigid-flex printed circuit board 10, and the rigid-flex printed circuit board 10 is manufactured by the production method provided by the invention.

It will be apparent to those skilled in the art from this disclosure that various other changes and modifications can be made which are within the scope of the invention as defined in the appended claims.

Claims

1. The production method for improving the flatness of the COB product of the rigid-flex printed circuit board is characterized by comprising the step of breaking a copper layer (20) of a waste area at a certain distance; and adjusting the flexible board (33) extending out of the rigid board (30) to a structure of five heads and two tails;

the structure of the first five tail parts is specifically as follows: a flexible plate (33) extends from the middle of the top end of the head part (31) of the rigid plate (30) far away from the tail part (32), and two flexible plates (33) symmetrically extend from the left end and the right end to form a head five; two flexible plates (33) symmetrically extend from the left end and the right end of the tail part to form a tail II;

the flexible plates (33) extending from the rigid plates (30) are respectively used for connecting the adjacent rigid plates (30).

2. The production method for improving the flatness of a flex-rigid board COB product according to claim 1, characterized in that the interval distance between the breaking of the copper layer (20) in the scrap area is 22-28 mm.

3. The method for improving the flatness of a flex-rigid board COB product as claimed in claim 2, wherein the copper layers (20) of the scrap area are broken by a distance of 25mm.

4. The method for improving the flatness of a flex-rigid board COB product according to claim 1, characterized in that the width of the copper layer (20) of the scrap area is broken to be 3-5 mm.

5. The method for improving the flatness of flex-rigid board COB products as claimed in claim 4, characterized in that the width of the copper layer (20) of the scrap area is 4mm.

6. The method for improving the flatness of a flex-rigid board COB product according to claim 1, characterized in that a dummy window (21) is provided at a position where the copper layer (20) is broken in the scrap area when the solder resist ink layer is made.

7. COB product as claimed in any one of claims 1 to 6, characterized by being produced by the production process as claimed in any one of the claims.